The invention relates to a process for producing a metal strip using a two-roller casting device, and to a two-roller casting device for carrying out the process. It is preferable for a two-roller casting device of this type to be used for the production of a steel strip of low thickness, in particular in a thickness range from 1.0 mm to 10 mm.
The central component of a two-roller casting installation is formed by two oppositely rotating casting rollers with casting-roller axes arranged parallel to one another, and two side plates which bear against the opposite end sides of the casting rollers. The distance between the two casting-roller axes is set such that the lateral surfaces of the casting rollers form a substantially parallel casting gap which corresponds to the casting thickness of the metal strip that is to be cast. The lateral surfaces of the interacting casting rollers and two end sides of the side plates form a space, which is closed in the peripheral direction, for receiving the metal melt, which is supplied via an inlet, solidifies at the cooled lateral surfaces of the casting rollers and is conveyed out of the casting gap in the form of an at least substantially fully solidified metal strip. An installation of this design and function is already known, for example, from WO 98/04369.
The end sides of the casting rollers lie in parallel planes with low tolerances. The side plates bearing against the end sides of the casting rollers consist of refractory material and are embedded in a carrying frame which is part of a side plate manipulator or of a supporting and carrying apparatus for the side plates. Numerous embodiments of devices of this type are known, for example from EP-A 714 715 or EP-B 620 061.
The side plates, which are made from refractory material, are pressed onto the end sides of the casting rollers with a predetermined pressure in order to ensure that they bear tightly against these end sides. The side plates are exposed to high and locally differing mechanical and thermal loads. In the melt pool and in the region of the casting gap there is direct contact with the metal melt and therefore considerable thermal and/or chemical wear; in the region of the contact surface between side plates and end sides of the casting rollers, the wear is predominantly mechanical on account of the movement of the components relative to one another under pressure and at elevated temperature. To minimize the overall wear and to increase the service life of the side plates, there are known solutions in which the side plates are made from different materials according to the particular local requirements (WO 98/04369).
To compensate for the wear and to maintain sealed bearing, the side plates, according to the prior art, are pressed onto the casting roller surface or moved continuously toward the casting roller lateral surface.
In the embodiment of a two-roller casting device of the generic type, as is known, for example, from EP-A 714 715 or EP-B 620 061, side plates which have been moved onto the end sides of the casting rollers are continuously held under contact pressure. The side plates are continuously worn away during the production cycle as a function of the set contact pressure and the casting rate, and this limits the duration of casting which can be achieved. A further unpleasant process engineering side-effect of this arrangement is the production of wear marks on the contact surface between side plates and solidified strip shell.
By contrast, EP-B 285 963 or EP-B 380 698 has disclosed, for a different arrangement of casting rollers and side plates, placing the refractory side plates, over a partial region of their thickness, on a narrow edge strip of the casting rollers and moving the side plate toward the casting gap at a predetermined feed rate during the casting operation. According to the design solutions described, the side plates are fixed on a carrier plate or guided in a frame and are moved onto the casting rollers by a spindle drive, a rack or similar mechanical means. The casting rollers are covered with wearing plates at their end sides, which ensure corresponding abrasion without the expensive casting rollers themselves being subject to wear from the side plates. On the one hand, the encircling contact grooves between wearing plates and side plates have an adverse affect on the formation of the edges of the strip, on account of the different temperatures of the two components, and on the other hand end-side sealing of the melt space is insufficiently ensured on account of the exclusively mechanical vertical guidance of the side plates.